1. Field of the Invention
The present invention relates to a fuzzy controller.
2. Description of the Prior Art
Reasoning rules and membership functions are essential to fuzzy control. Fuzzy control by microcomputers is currently used to control various appliances. In the microcomputers, the reasoning rules and membership functions are realized by means of software.
According to a currently-used method of fuzzy control by the microcomputers, a control signal is produced as a result of fuzzy reasoning based on a reasoning rule and a membership function while the reasoning rule and membership function are being produced based on an input data representative of a phenomenon of, for example, an appliance to be controlled. The results of calculation to find a minimum value and a maximum value of the input data are successively stored in a random access memory (RAM). It is very easy to design software to specify how each result stored in the RAM is related. Such software corresponds to the determination of the membership functions. Thus, the membership functions are easily realized by means of software.
As the reasoning rule, for example, whether multiplication or division is performed is determined. Since in the microcomputers this corresponds to the determination of which instruction to use, the reasoning rules are also easily realized by means of software.
In the case of fuzzy control by means of software, however, the processing speed is low since the processing by means of software is constituted by many processing steps. Although the low processing speed does not matter in appliances such as washing machines and air conditioners not requiring very high control speed, it presents problems when the fuzzy controller is used for high-speed control such as the high-speed plant control and the control to produce optima for a chemical reaction, since the low-speed fuzzy control cannot cope with such plant processing and chemical reaction.
Therefore, to cope with such high-speed control, it is preferable to realize the reasoning rules and membership functions by means of hardware. In conventional hardware fuzzy controllers, the reasoning rules and membership functions are stored in a read only memory (ROM).
However, to store the reasoning rules and membership functions, large-capacity ROMs are required. This increases the size and hinders the realization of a one-chip fuzzy controller.